Anabolic Androgenic Steroid (AAS) use affects about 1-3% of the population and is an issue of great social, academic, and medical interest. AAS use is associated with increased rates of violent death (homicide/suicide) and earlier age of death than other illicit drug-using populations, and exhibits a significant rate of dependency among users. Medical consequences may include increased risk for cardiac events, liver toxicity, skeletal changes, and hypothyroidism, and overall higher mortality and morbidity. Currently, there are no treatments for AAS dependence or intoxication. As a first step, characterizing the neurobiological changes associated with AAS intoxication will be essential to the development of novel and effective therapeutics designed to treat AAS dependence and limit the psychiatric consequences to AAS use. The proposed study aims to identify some of the key neurobiological processes responsible for AAS intoxication in a group of active and experienced AAS- using men. By studying AAS intoxication in relation to aromatase availability, we will be able to understand functional relationships between AAS metabolism and the core psychological and behavioral changes that reinforce AAS use. Although AASs are taken primarily for their ability to change appearance or increase athletic performance, the AAS intoxication syndrome can be defined by the desirable psychological and behavioral effects of AAS use that include increases in social dominance, sex drive, aggression, goal directed behavior, and self-esteem, which all share a common increase in behavioral disinhibition. The study aims to examine two novel hypotheses: 1) AAS users will have higher levels of brain aromatase than controls, and will have further elevated levels when taking AASs; 2) Regional brain aromatase availability will be positively correlated with behavioral and self-report measures of impulsivity, aggression, and sensitivity to pleasure. Two specific aims were developed to test these hypotheses: A) To evaluate the effect of AAS use on regional brain aromatase availability in relation to circulating gonadal hormone levels; B) To test for a correlation between change in regional brain aromatase availability and behavioral measures of the AAS intoxication syndrome (aggression, sexual activity, impulsivity, and sensation seeking) in AAS users. These aims will be tested in a controlled longitudinal study of male AAS users (n=8) and healthy exercising controls (n=8) matched on age, exercise, and education. The results of this study will be used as pilot data for a longitudinal study of AAS dependence in which we will examine the changes in aromatase as a function of repeated AAS use. This line of research will be aimed at developing biomarkers and investigating individual differences in AAS response among real world AAS users. The proposed study will also provide data to develop novel therapeutic targets to prevent and treat AAS addiction; specifically, aromatase inhibitors and estrogen antagonists may be used as pharmacological agents to treat AAS intoxication. These outcomes are in concordance with NIDA's goals to directly inform prevention and treatment efforts in this population.